JRA-55C¶
The Japanese 55-year Reanalysis Using Conventional Data Only (JRA-55C)
Discontinued
No longer updated
A completed, fixed-period dataset (November 1972 – December 2012) that will not be extended. It is not a 20th-century reanalysis but a "fixed observing system" experiment: the JRA-55 system run without satellite observations, assimilating only conventional surface and upper-air observations. It is used to study long-term homogeneity free of artificial changes caused by the introduction of satellite data; no JRA-3Q-based successor of the same kind has been identified.
At a glance¶
| Item | Details |
|---|---|
| Section | Atmosphere › Reanalyses without satellite data |
| Type | Reanalysis |
| Domains | Atmosphere |
| Provider | Meteorological Research Institute, Japan Meteorological Agency (JMA/MRI) |
| Period | 1972-11 ~ 2012-12 |
| Coverage | Global |
| Horizontal resolution | Model resolution TL319 (about 55 km, same as JRA-55) / 1.25° × 1.25° (288 × 145) and 2.5° × 2.5° (144 × 73) latitude-longitude grids / about 0.5625° Gaussian grid (640 × 320) |
| Vertical resolution | 60 model levels / 37 pressure levels |
| Temporal resolution | 6-hourly analyses, 3-hourly forecasts and diagnostics (monthly means and variances provided separately) |
| Update frequency | Ended (fixed-period dataset) |
| Licence | CC BY 4.0 (as stated by NCAR GDEX) + JMA terms of use (no commercial use, no redistribution without JMA's consent, copies of publications to JMA) |
| Account required | Yes |
Note on period: JRA-55C itself runs from November 1972 to December 2012. The data for January 1958 to October 1972 are exactly the same as JRA-55 (no satellite data existed then), so JMA recommends using JRA-55 for that period to form a 1958–2012 series.
How to read the resolution
- Horizontal resolution lists both the native model grid and the grid you download, as given in the official documentation. The same dataset can come on different grids from different providers or products, so check the grid of your downloaded file.
- Grid spacing is not the effective resolution. A provided grid that is finer than the native one carries no extra information.
- Intervals and whether a value is instantaneous, mean or accumulated differ between variables — see 'Available variables' below.
- The 'provided resolution' in lists and the comparison table is a simplified km/degree value for quick comparison. Use this page for exact values.
Overview¶
A global atmospheric reanalysis by the JMA Meteorological Research Institute that uses the same 4D-Var data assimilation system as JRA-55 but assimilates only conventional surface and upper-air observations, with no satellite data. Despite "55-year" in its name it does not reach back to the early 20th century; its purpose is to produce a more homogeneous dataset over a long period, separating spurious trends caused by changes in the observing system (above all, the arrival of satellites) and checking the homogeneity of multidecadal variability. As a best estimate for the data-rich period after 1979 it is inferior to JRA-55, so it is used alongside JRA-55 for the same period.
Available variables¶
Main variables from the JRA-55 Product Users' Handbook and the NCAR GDEX (d628002) file names. The variables and their names are the same as JRA-55, with ".C." added to the GDEX file names (e.g. anl_p25.C.011_tmp → tmp). Precipitation and evaporation are mean rates in mm/day.
Time-stamp convention — instantaneous, mean or accumulated? — click to show
Same conventions as JRA-55. Analyses (anl_*) are 6-hourly instantaneous values; forecast-averaged diagnostics (fcst_phy2m) are 0–3 h and 3–6 h averages from forecasts started every 6 hours, and the date in the original file names is the start of the averaging interval. Precipitation and evaporation are mean rates over the interval (mm/day), not accumulations.
- Analysis products (anl_p, anl_surf) are instantaneous values at 00, 06, 12 and 18 UTC.
- fcst_phy2m holds 3-hour averages: the first interval (e.g. 00–03 UTC) is the 0–3 h forecast average and the second (e.g. 03–06 UTC) the 3–6 h forecast average.
- For averaged variables, the date in the original file name is the start of the interval (e.g. 2012010100 = 00–03 UTC average). This is the opposite of JRA-25 — take care.
- fcst_p (cloud, ozone) is 6-hourly forecast output with no averaging interval indicated; treat it as instantaneous.
- The NCAR GDEX THREDDS aggregations include the averaging interval in time_bounds.
Source: JRA-55 Product Users' Handbook (JRA-55C has the same product structure)
instantaneous mean accumulated maximum minimum static — instantaneous: value at the time stamp · mean/accumulated/maximum/minimum: over the indicated interval · static: does not change with time
Pressure-level analysis (anl_p, 6-hourly)¶
| Variable | Short name | Units | Time convention | Notes |
|---|---|---|---|---|
| Geopotential height | hgt |
gpm | instantaneous (6-hourly) | |
| Temperature | tmp |
K | instantaneous (6-hourly) | |
| u-component of wind | ugrd |
m s-1 | instantaneous (6-hourly) | |
| v-component of wind | vgrd |
m s-1 | instantaneous (6-hourly) | |
| Vertical velocity (pressure coordinate) | vvel |
Pa s-1 | instantaneous (6-hourly) | |
| Specific humidity | spfh |
kg kg-1 | instantaneous (6-hourly) | |
| Relative humidity | rh |
% | instantaneous (6-hourly) | |
| Stream function, velocity potential | strm, vpot |
m2 s-1 | instantaneous (6-hourly) |
Surface analysis (anl_surf, 6-hourly)¶
| Variable | Short name | Units | Time convention | Notes |
|---|---|---|---|---|
| Surface pressure | pres |
Pa | instantaneous (6-hourly) | |
| Pressure reduced to MSL | prmsl |
Pa | instantaneous (6-hourly) | |
| 2 m temperature | tmp |
K | instantaneous (6-hourly) | |
| 2 m specific humidity | spfh |
kg kg-1 | instantaneous (6-hourly) | |
| 10 m u- and v-component of wind | ugrd, vgrd |
m s-1 | instantaneous (6-hourly) |
Fluxes and diagnostics — 3-hour forecast averages (fcst_phy2m)¶
| Variable | Short name | Units | Time convention | Notes |
|---|---|---|---|---|
| Total precipitation | tprat |
mm day-1 | 3-hourly mean | |
| Convective and large-scale precipitation | cprat, lprat |
mm day-1 | 3-hourly mean | |
| Evaporation | evp |
mm day-1 | 3-hourly mean | |
| Latent and sensible heat flux | lhtfl, shtfl |
W m-2 | 3-hourly mean | |
| Downward shortwave and longwave radiation flux (surface) | dswrf, dlwrf |
W m-2 | 3-hourly mean | |
| Upward shortwave and longwave radiation flux (surface and top of atmosphere) | uswrf, ulwrf |
W m-2 | 3-hourly mean |
Cloud and ozone (fcst_p, 6-hourly)¶
| Variable | Short name | Units | Time convention | Notes |
|---|---|---|---|---|
| Total cloud cover | tcdc |
% | instantaneous (6-hourly) | Cloud cover on pressure levels in fcst_p. The handbook does not state that it is instantaneous, and the GDEX metadata give no averaging interval |
| Ozone mixing ratio | ozone |
mg kg-1 | instantaneous (6-hourly) | The handbook does not state that it is instantaneous, and the GDEX metadata give no averaging interval |
The full variable list is in the official documentation.
How to get the data¶
- NSF NCAR GDEX — 3-hourly and 6-hourly data (d628002) — Web download / THREDDS
- Requires NCAR registration (and acceptance of the JRA-55 terms). GRIB1, reorganised into single-parameter time series files.
- NSF NCAR GDEX — monthly means and variances (d628003) — Web download
- DIAS — JRA55_C — Web download
- Requires a DIAS account. JRA-55C is not yet on the republication list published after DIAS's extended 2026 maintenance (checked October 2026), so it cannot currently be downloaded there. Use NCAR.
Practical tips¶
- If you need data before October 1972, follow JMA's recommendation and append JRA-55 for that period; the two datasets are identical there.
- Compare trends side by side with JRA-55, which uses the same system. The difference between the two is a clue to the impact of introducing satellite observations.
- Uncertainty is large over the oceans, at high southern latitudes and in the upper stratosphere, where observations are sparse. A dry bias in the upper and middle troposphere, an artificial weakening tendency of tropical cyclone intensity, and a discontinuity over Africa around 1998 have also been reported.
- If you downloaded the January–August 2005 files from DIAS before 23 March 2016, you have the erroneous version and must download them again.
Notices and change history¶
2016-03-23 · Warning · January–August 2005 files replaced (DIAS)
Part of the JRA-55C data from January to August 2005 on DIAS included an error, and the erroneous data were replaced with corrected data on 23 March 2016. Files for that period downloaded before then must be downloaded again.
2015-07-28 · Info · JRA-55C in the RDA: The Japanese 55-year Reanalysis Using Conventional Data Only
NCAR downloaded the full JRA-55C archive, reorganised it into single-parameter time series, and began releasing it incrementally to registered JRA-55 users of the RDA.
References for your paper¶
Double-check before using in a paper
The citations below were compiled by the maintainer and may contain errors. Always double-check DOIs, authors, years and access-date formats against the provider's official dataset page and your journal's guidelines.
Dataset citation¶
NCAR GDEX 3-hourly and 6-hourly data (d628002) — DOI 10.5065/D67H1GNZ
Japan Meteorological Agency (2015): JRA-55C: The Japanese 55-year Reanalysis Using Conventional Data Only. Research Data Archive at the National Center for Atmospheric Research, Computational and Information Systems Laboratory. https://doi.org/10.5065/D67H1GNZ (Accessed DD MMM YYYY)
Show BibTeX
@misc{jra55c_d628002,
author = {{Japan Meteorological Agency}},
title = {{JRA-55C}: The Japanese 55-year Reanalysis Using Conventional Data Only},
year = {2015},
publisher = {Research Data Archive at the National Center for Atmospheric Research, Computational and Information Systems Laboratory},
doi = {10.5065/D67H1GNZ},
note = {Accessed DD MMM YYYY}
}
NCAR GDEX monthly means and variances (d628003) — DOI 10.5065/D6C827B7
Japan Meteorological Agency (2015): JRA-55C: Monthly Means and Variances. Research Data Archive at the National Center for Atmospheric Research, Computational and Information Systems Laboratory. https://doi.org/10.5065/D6C827B7 (Accessed DD MMM YYYY)
Reference papers¶
JRA-55C preliminary results paper — DOI 10.2151/sola.2014-016
Kobayashi, C., Endo, H., Ota, Y., Kobayashi, S., Onoda, H., Harada, Y., Onogi, K., Kamahori, H. (2014): Preliminary Results of the JRA-55C, an Atmospheric Reanalysis Assimilating Conventional Observations Only. SOLA, 10, 78–82.
Show BibTeX
@article{kobayashi2014jra55c,
author = {Kobayashi, Chiaki and Endo, Hirokazu and Ota, Yukinari and Kobayashi, Shinya and Onoda, Hirokatsu and Harada, Yayoi and Onogi, Kazutoshi and Kamahori, Hirotaka},
title = {Preliminary Results of the {JRA-55C}, an Atmospheric Reanalysis Assimilating Conventional Observations Only},
journal = {SOLA},
volume = {10},
pages = {78--82},
year = {2014},
doi = {10.2151/sola.2014-016}
}
JRA-55 reference paper (describes the data assimilation system) — DOI 10.2151/jmsj.2015-001
Kobayashi, S., Ota, Y., Harada, Y., Ebita, A., Moriya, M., Onoda, H., Onogi, K., Kamahori, H., Kobayashi, C., Endo, H., Miyaoka, K., Takahashi, K. (2015): The JRA-55 Reanalysis: General Specifications and Basic Characteristics. J. Meteor. Soc. Japan, 93(1), 5–48.
Acknowledgements¶
Under the JMA terms of use, the source of the data must be duly acknowledged in papers and presentations, and a copy of the resulting publication sent to JMA (jra@met.kishou.go.jp). JMA's example wording is "The dataset used for this study is from the Japanese 55-year Reanalysis Using Conventional Data Only (JRA-55C) project carried out by the Japan Meteorological Agency (JMA)"; see the terms of use on the NCAR GDEX dataset page for the full text.
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